By this point, I’ve seen enough let’s-go-to-Vegas-for-one-last-fling comedies until they are practically coming out my ears. The strains of going to Sin City for a hedonistic bacchanal bachelor party has some naughty allure but it’s been done so many times that it has become a cliché wrapped inside of itself. Nothing ever goes as planned. Vegas is promoted as such a hotbed of sin and vice, yet it’s so regulated and organized that the reckless nature of our heroes comes from outside disasters. Yes, someone can get hammered, lose all their money at the craps table and then end up marrying a hooker at The Chapel O’ Love who will refuse to get an annulment, but it’s not really the fault of Vegas being a modern-day Sodom and Gomorrah. These things happen cuz peeple be stoopid. They could happen anywhere. Vegas just happens to have a rep. But this particular set of scenerios has been done so many times that they are as telegraphed as a bus schedule.

That’s a nice way of saying, I didn’t walk into The Hangover last Tuesday morning with a heart full of enthusiasm. This is the latest from Todd Phillips, the mind behind Frat House, Road Trip and Old School; all movies that I walked away from with relative indifference.

To my surprise, this time he got it absolutely right. The movie turns out to be one of the nicest surprises of the year. It’s very funny. It’s clever. It offers a premise that we care about. It offers a premise that is reasonably plausible. And again, it’s very funny.

What is different about The Hangover is that it takes the Vegas-romp scenario in an intriguing direction, setting it up like a mystery that is solved piece by piece. Our quartet of heroes arrive in Vegas from L.A. for a bachelor party thrown for their buddy Doug (Justin Bartha), but they’re not exactly party animals. They’re un-extraordinary schmoes who have spent more time thinking about cutting loose than actually doing it. It’s almost like they’ve seen all those let’s-go-to-Vegas-for-one-last-fling comedies and decided to give it a try.

The leader of the group is Phil (Bradley Cooper), a good-looking Junior High School teacher who is married with kids, but apparently misses the old days. There’s Stu (Ed Helms), a dork-ish square who lives with a hate-spewing girlfriend who treats him like a doormat. And there’s Alan (Zach Galifianakis). Alan is . . . well, I dunno. He is Doug’s block stupid brother-in-law-to-be whose personality is so off-kilter that you’re not sure if he is suffering a mental disorder or maybe he stepped out of a cartoon. When the gang arrives at Caesars Palace, he asks the check in girl, “Did Caesar live here?”

The movie’s first 20 minutes are, I will confess, kind of dull. It’s all set-up and nothing that happens is all that memorable, but then the plot kicks in. The gang gathers on the roof of their hotel for a final toast and then . . . . well, from there it’s all a big blank. The guys wake up the next morning in a trashed $4,000-a-night hotel room and can’t remember a thing. Something obviously happened the night before but the evidence doesn’t offer connective clues: There’s a baby in the cabinet. There’s a tiger in the bathroom. There’s a chicken running around. Stu is missing one of his incisors. Alan has his belly button pierced. And when they call for their car, the valet brings around a police car. Oh yeah, and Doug is missing.

The rest of the movie follows the same pattern of Martin Scorsese’s underappreciated After Hours wherein the insanity of the night comes into focus. The mission becomes an all-consuming investigation as the remaining trio try and gather clues to their activities the previous night in an effort to locate their friend and (literally) get him to the church on time. What ensues in a comic nightmare in which the boys run into one damned thing after another – a cosmic punishment, perhaps, for their hedonism.

What comes of these punishments are the meat of the story so I’ll be as vague as I can. There’s a wedding chapel, a naked Asian man with a crowbar, a mean-spirited emergency room tech whose bedside manner could use some fine-tuning, a police taser lesson, and a run in with Mike Tyson. The greatness of The Hangover is the way in which it starts slow and ordinary and then builds its story brick by brick and actually gets funnier as it goes along. That’s a nice contrast when you consider that most comedies of this sort do just the opposite – they start off with promise but run out of gas fairly early on.

Plus, actually care what is going on. The movie has a raunchy side but it’s not front and center. Phillips wants this story to build so that the comedy comes from that and not trying for gross-out gags. Plus, we care about these guys. They are played by actors that I am unfamiliar with. We like them, particularly Stu whose a successful dentist but is on the cusp of marrying a woman who will suck out his life force. Ed Helms plays him as the put-upon dork who needs this weekend in Vegas to break out of his neurotic state of denial. Bradley Cooper, as Phil, is offered the kind of role that promises great things to come – he’s a heartthrob in the making. And Galifianakis? I’m not 100% sure what to make of him. He seems so weird that he almost seems to have been flown in from another movie. He says and does things that no human being on Earth would ever do and I was perplexed as to whether it’s a stand-out or a draw back.

The characters aren’t fleshed out, though to do care about them. They’re closer to types than to flesh and blood, and I think that’s the film’s one missing element. In order for this film to tip over into greatness the guys needed just a touch more humanity, just a little bit more of the old El Corazon and I think the comedy could be just as heartfelt as it is funny.

Still, I’ll be thinking about this movie when it’s imitators are just going through the motions. I’ll be thinking about the great mystery game it lays out. I’ll be thinking about how they solved it. I’ll still be wondering why there was a chicken in the room. No one ever figured that one out.